The purification of waste water and the rendering innocuous of waste solids is an important part of virtually every modern industrial process. In particular, much effort has been expended in recent years in insuring that the risk of pollution is minimized by the treatment of waste water before it is discharged into rivers, lakes, and other waterways and to eliminate future risks associated with waste solids. Another important reason for the treatment of waste water is that it enables the water to be recycled for use in the industrial process, allowing more efficient use of water and reducing the economics of the industrial process by reclaiming materials that would otherwise be discarded. The environmental problems associated with industrial chemical processes has led industry into a position wherein no materials adversely affecting the environmental process should be discharged into the water cycle of the earth.
This invention relates to the treatment of waste waters and solids produced in a process for the manufacture of phosphorus pentasulfide, and enables the water to be recycled through the process and allows for its safe discharge into streams, rivers, or lakes.
Phosphorus pentasulfide is manufactured by reacting elemental phosphorus with molten sulfur in approximately stoichiometric proportions. The crude product is usually distilled and cast into molds or cast in a thin film on a cold surface. The product may be distilled and quick chilled under inert gases to obtain a more reactive form. Phosphorus pentasulfide (P.sub.4 S.sub.10) melts in the range 286.degree.-290.degree. C. and boils at 513.degree.-545.degree. C. It is a reddish brown in liquid form and yellow in solid form. It is slowly decomposed by cold water and forms mainly hydrogen sulfide and orthophosphoric acid. At high pH it is hydrolyzed to a mixture of products containing thiophosphates and sulfides. Exact reactions of hydrolysis are imperfectly understood and sensitive to system changes.
There are four major sources of solids and contaminated water from a phosphorus pentasulfide manufacturing facility that constitute the bulk of the waste water. These are water used in washing equipment and returnable shipping bins, fume scrubbers, water from pouring station scrubbers, water from dust scrubbers and water from roofs, drains, rain, etc. which contain amounts of phosphorus pentasulfide as a result of contact with the solid.
Prior to environmental restrictions imposed by state and federal agencies, the industrial waste water was generally collected in a storage facility such as a pond or tank to allow any solid material to settle out, and the liquid then was discharged. The solid materials were transferred to a burial site. With environmental restrictions imposed upon industry, the water discharged into streams, rivers, and lakes must be essentially pure and non-polluting and should not affect the oxygen balance of the waterway. This has led to purification systems, material recovery systems, and the recycling of water within the industrial plant. The invention described in this document concerns the waste treatment system for a phosphorus pentasulfide facility, and the rendering innocuous of phosphorus pentasulfide contained within the stream entering the waste treatment process.
It is the object of this invention, therefore, to provide an effective treatment for all sources of phosphorus pentasulfide waste associated with a phosphorus pentasulfide manufacturing process, to chemically transform its phosphorus and sulfur content so that essentially pure water can be discharged into the environment and a solid containing essentially calcium phosphate, gypsum and elemental sulfur can be generated for safe landfill. Further, no forms of airborne sulfur or phosphorus based contaminants should emanate from the process.
It is also an object of this invention to provide a treatment process for the purification of water associated with waste treatment to allow its recycling back into the plant for further use.